Crabapple bark split
While raking leaves I noticed a large bark split on north-facing side of my Royal Raindrops crabapple in St. Paul, MN. Older scars nearby are smaller and appear well-healed. What could have caused this? Do I need to do anything to protect the area for the winter? Recommendations? I chose this variety in part because it was supposed to be highly disease resistant across major categories.
Ramsey County Minnesota
Bark splitting can be caused by many things. In fact, some varieties of crabapple exfoliate their bark naturally. I'm ruling out the most common cause of bark splitting in your case - sunscald - because it is on the north side and the tree is mature. If the tree is otherwise healthy, you can "treat" it by trimming away the exfoliated bark. Read here:
I am more concerned about the branching of your tree. Your tree has three co-leaders emerging from a single junction and your tree has a lot of included bark at that junction. This all makes for a very weak junction, giving me some concern about the overall health of the tree. It is also noteworthy that the vertical crack is directly above this junction. I'd have a certified arborist assess your tree:
Read here about poor branching: